1. Field of the Invention
This invention relates to a roller bearing adapted to be incorporated properly into the gearings included in the transmissions or differentials of automobiles.
2. Brief Description of the Prior Art
In recent years in automobile transmissions or differentials and other areas where roller bearings are used, there have been steady advancements in size reduction and high output power attainment, and there has been a tendency for service environments that include the use of low viscosity lubricating oil to go to a high load high temperature side. For this reason, lubrication environments are becoming more severe than before, tending to cause more and more surface originated flaking due to poor lubrication.
Japanese Laid-Open Patent Specification Nos. Heisei 2-168021 and Heisei 6-42536 disclose roller bearings having minute irregularities formed in the surfaces of rolling elements to improve the oil film forming ability. These conventional minute, recess-shaped cavities are sized such that when the surface roughness is expressed by a parameter Rqini, the value of the ratio, Rqini (L)/Rqini (C), where the Rqini (L) is the axial surface roughness and the Rqni (C) is the circumferential surface roughness, is not more than 1.0 (Rqini≧0.10) and at the same time the parameter Sk value of surface roughness is not more than −1.6, so as to ensure long life irrespective of whether the mating surface is a rough surface or a good finished surface. However, there are cases where the effects cannot be fully exerted if the oil film thickness is extremely low under low viscosity, lean lubrication conditions.